Fluid handling apparatus for use as vacuum pump



Feb 1967 J. P. WREDE 3,302,868

FLUID HANDLING APPARATUS FOR USE AS VACUUM PUMP Filed March 29, 1965 3-Sheets-Sheet l 3 f 1k, '1 x 62 g, I at 5 """/Q A/ 6 z 7' l 11 l 6 Inventor:

Feb 7, 1967 J. P. WREDE 3,302,868

FLUID HANDLING APPARATUS FOR USE AS VACUUM PUMP Filed March 29, 1965 3 Sheets-Sheet 2 INVENTOR JURGEN PETER WREDE Feb, 7, 1967 J. P. WREDE 3,302,868

FLUID HANDLING APPARATUS FOR USE AS VACUUM PUMP Filed March 29, 1965 3 Sheets-Sheet 3 H64 H65 FIG.6

INV EN TOR Ji'JRGEN PETER WREDE United States Patent 3,302,868 FLUID HANDLING APPARATUS FOR USE AS VACUUM PUMP Jiirgen Peter Wrede, Euskirchen, Germany, assignor to E. Leybolds Nachfolger, Cologne-Bayental, Germany Filed Mar. 29, 1965, Ser. No. 443,574 Claims priority, application Germany, Apr. 2, 1964, L 47,474 4 Claims. (Cl. 230141) This invention relates to vacuum pumps of the rotary positive displacement type.

The Roots type pump has been in use for many years for producing vacua and high vacua. As no liquid sealing material may be used between the impellers and the internal walls of the pump housing the ratio of input power to the available capacity does not exceed 15% on average, rising to a maximum of 25% in exceptional cases. Moreover the useful working life of such a pump is adversely affected in course of time by the regular pressure peaks that occur between the impellers.

This invention provides an impeller pump with at least two impellers, which overcomes the limitations heretofore encountered.

The principal object of this invention is to provide an improved form of impeller which gives better ratio of input power to the available capacity.

Another object of this invention is the reduction of pressure peaks to the shafts on which the impellers are mounted.

A further object of the invention is to provide an impeller pump of smaller dimension than heretofore pos sible, which allows an extension of the applicability of this type of pump for producing vacua.

These and other objects of the invention will appear more fully upon consideration of the detailed description of the embodiment of the invention. Although only some embodiments of the invention are described and illustrated, it is to be expressly understood that these drawings are for purposes of illustration only and are not to be construed as defining the limits of the invention.

In the drawing, FIG. 1 shows a diagrammatic sectional view of a Roots type impeller pump, FIG. 2 shows the same pump, showing two particular embodiments of the invention, FIG. 3 shows a view of the pump with the shafts passing through the housing for connection to driving and exhausting means, FIGURES 4 through 12 showing specific configurations of the arrangement of openings on the periphery of the lobes of the pump. In the drawings 1 is the pump housing with the inlet 2 and outlet 3. Two parallel and laterally spaced shafts 4, 5, one or more of which may pass through the housing suit- :ably sealed vacuum-tight in a manner known to the art, are journalled in the housing 1. The impellers 6, 7, which in the illustration shown are of the lobe type are mounted on each shaft before mentioned, mesh as the shafts are rotated and sweep the medium (gas, vapor) to be pumped from the inlet 2 to the outlet 3. As the impellers rotate pressure peaks are formed regularly in the area shaded and marked 8, 81. It has been found that the volumetric efiiciency of an impeller pump is improved to several times the value that was attainable heretofore and that, therefore, the output can be raised considerably without simultaneously raising the input power by providing the external periphery 61, 71 of 3,302,868 Patented Feb. 7, 1967 the impellers 6, 7 with openings 62, 63 and 72, 73 communicating with the internal cavities as shown in FIG. 2, with communication between the cavities and an external vacuum pump through slots 5 and hollow shaft 5 or, as shown in the right-hand impeller of FIG. 2, by directly connecting openings 62, 63 and 72, 73 by tubular members 64 to the hollow shaft 5, the latter again being connected to a vacuum pump in a manner known to the art and shown in FIG. 3. Particularly with smaller vacuum pumps and when the cavities in the impellers are required for cooling or other purposes I have found it appropriate and advantageous to use the latter structure, i.e., to connect the openings 62, 63 and 72, 73 directly to the hollow shafts 4, 5.

As a result of this arrangement that portion of the medium to be pumped which tends to escape into the higher pressure region through the clearance 81 between the impellers 6, 7 is intercepted and drawn off through the openings 62, 63 and 72, '73 into the internal cavities. For the evacuation of the hollow shaft 5, tubular members 64 and the cavities formed by hollow impellers 6, 7 any type of vacuum pump, whose performance is low in relation to the performance of the impeller pump, can be used.

Moreover, since the pressure peaks that build up between the impellers are drawn off, the life of the pump is prolonged because the transient loads on the bearings and shafts of the impellers are lessened.

I have also found that the final vacuum attainable with an impeller pump according to the present invention can be substantially improved.

In order to obtain optimum results I have further found that the openings 62, 63 and 72, 73 should preferably extend over a region extending from 30 ahead of to 60 beyond the vertex of the lobe measured in the direction of impeller revolution.

Ideally the openings 62, 63 and 72, 73 should be slits extending across the full width of the impeller periphery 61, 71. Since this is impossible for structural reasons it has been found useful to extend the circular, semicircular, pear-shaped or angular openings across at least two-thirds of the width of the impeller some of the configurations which have been found particularly useful are illustrated in FIGURES 4 through 12.

It will be obvious that the invention is not limited to this example but is capable of a variety of mechanical and procedural embodiments.

The invention having now been fully described and disclosed, that which I claim as new is:

1. In a vacuum pump of the kind described, in combination a housing with inlet and outlet openings, at least two intermeshing rotatable lobed type impellers, hollow shafts on which said lobed type impellers are mounted, said impellers provided with openings which communicate with the cavities of the impeller and/or the shafts, said shafts provided with means to connect to a vacuum pump and a vaccum pump to draw off any medium which may be entrapped between said impellers or said impeller and said housing.

2. A pump as set forth in claim 1, wherein the openings are located within a region extending from 30 ahead of to 60 behind the vertex of the lobe in the direction of rotation of the impeller.

3. A pump as set forth in claim 2,. wherein said openings are of circular, semicircular, pear-shaped or angular 3 4- configuration and openings extend across at least two- 2,259,027 10/1941 De Zarate et a1. 230141 thirds of the Width of the impeller. 2,484,917 10/ 1949 Vertson 103--126 4. A pump as set forth in claim 3, in which said open- 2,938,664 5/1960 Noller 230-141 ings are provided in only one of the impellers of the 3,077,839 2/1963 Gondek 103126 PumP' 5 FOREIGN PATENTS References Cited by the Examiner UNITED STATES PATENTS 1 192 73 1933 Svenson 103 12 DONLEY J. STOCKING, Primary Examin r.

2,029,742 2/1936 i v r 1 126 10 LB J, GOODLIN, E i r,

7,593 1884 Great Britain. 

1. IN A VACUUM PUMP OF THE KIND DESCRIBED, IN COMBINATION A HOUSING WITH INLET AND OUTLET OPENINGS, AT LEAST TWO INTERMESHING ROTATABLE LOBED TYPE IMPELLERS, HOLLOW SHAFTS ON WHICH SAID LOBED TYPE IMPELLERS ARE MOUNTED, SAID IMPELLERS PROVIDED WITH OPENINGS WHICH COMMUNICATE WITH THE CAVITIES OF THE IMPELLER AND/OR THE SHAFTS, SAID SHAFTS PROVIDED WITH MEANS TO CONNECT TO A VACUUM 